A resonant pressure sensor and a method for preparing the same

Abstract

The present invention provides a resonant pressure sensor and a manufacturing method thereof, comprising the following steps: providing a substrate, and forming a pickup resistor and a drive resistor which are arranged at intervals on the upper surface layer of the substrate; forming at least one resonant structure including a resonant beam and a vibration gap on the upper surface layer of the substrate, the resonant beam comprising a first beam, a second beam and an intermediate beam which are connected, the drive resistor and the resonant resistor are respectively located on the upper surface layers of the first beam and the second beam, the vibration gap includes an etching groove surrounding the resonant beam and a bottom cavity located below the resonant beam and communicating with the etching groove; forming a sacrificial layer on the upper surface of the substrate to cover the opening of the vibration gap and the upper surface of the resonant beam and having an edge spaced from the opening of the vibration gap by a first preset distance, and a sealing shell covering the sacrificial layer; forming a groove opening from the bottom surface of the substrate directly below the resonant structure and having a bottom spaced from the bottom of the vibration gap by a second preset distance; the sealing shell and the vibration gap enclose a sealed cavity. The manufacturing method of the pressure sensor of the present invention reduces the production cost.

Description

Technical Field

[0001] The present invention relates to the field of silicon micromachining sensing technology, and in particular to a resonant pressure sensor and a preparation method thereof. Background Art

[0002] With the development of microelectromechanical system (MEMS) sensor technology, micromachined low-pressure sensors are widely used in industries such as aerospace, wearable devices, medical, and automotive electronics due to their advantages of light weight and small size. Currently, miniaturization, high precision, and cost reduction of sensors are an important development trend of MEMS technology. Compared with low-pressure sensors based on other mechanisms, such as piezoresistive low-pressure sensors and capacitive low-pressure sensors, resonant low-pressure sensors have better performance in terms of device sensitivity, stability, and accuracy because they allow digital output and are less affected by ambient temperature. Therefore, manufacturing miniaturized, high-precision, and low-cost low-pressure resonant pressure sensors will become a research hotspot.

[0003] The working principle of a resonant pressure sensor is to utilize the resonant frequency of a semiconductor resonator. The mechanical strain generated by pressure causes a change in the resonant frequency of the resonator. Through an appropriate circuit, this change is converted into a measurable signal output to determine the pressure. Currently, the main core components of a resonant pressure sensor are mainly composed of a pressure detection sensitive film and a resonant beam. In 1992, Tokuji Saigusa et al. from Yokogawa Electric in Japan designed and manufactured a silicon resonant differential pressure sensor fabricated using three-dimensional micro-machining technology, as well as an intelligent differential pressure transmitter using this sensor. This differential pressure transmitter has a relatively high overall environmental accuracy (T. Saigusa and H. Kawayama, “Intelligent differential pressure transmitter using micro-resonators,” in Proceedings of the 1992 International Conference on Industrial Electronics, Control, Instrumentation, and Automation, San Diego, CA, USA: IEEE, 1992, pp. 1634–1639. doi: 10.1109 / IECON.1992.254354.). By designing a differential structure, this sensor eliminates the small temperature coefficients of the two resonators, achieving relatively high temperature stability; by enclosing the resonator in a vacuum chamber, a high Q value is obtained, and it is insensitive to the contamination effects of ions and impurities. However, this sensor uses KOH anisotropic etching to form a diaphragm on the back of the substrate, and it takes a lot of time to use KOH solution to thin the silicon wafer over a large area and to a large depth to achieve the expected structural beam thickness, which prolongs the production cycle and increases the manufacturing cost. In 2021, Wang Junbo et al. from the Beijing Institute of Microelectronics, Chinese Academy of Sciences, designed and fabricated a resonant differential pressure sensor using bulk micromachining and silicon-on-insulator (SOI) processing technology, which can be used in a measurement range of hundreds of kilopascals (Y. Li et al., “A High-Sensitivity Resonant Differential Pressure Microsensor Based on Bulk Micromachining,” IEEE Sensors J., vol. 21, no. 7, pp. 8927–8934, Apr. 2021, doi: 10.1109 / JSEN.2021.3051286.).This sensor uses silicon deep reactive ion etching (DRIE) to fabricate the pressure-sensitive film, which shortens the processing time compared to fabricating the film by KOH etching. However, there are still the following deficiencies in fabricating the pressure sensor by this method: First, fabricating the pressure sensor through the SOI processing technology has problems of relatively complex manufacturing processes and long production cycles, which is not conducive to reducing the cost of a single sensor. Second, assembling the resonant beam and the sensitive film by alignment and anodic bonding easily introduces unnecessary mechanical strain to the device structure, which has an adverse impact on the yield and repeatability of device production. Third, when using the SOI (silicon-on-insulator) process, it is necessary to use heavy doping to fabricate the resistor, and it is impossible to fabricate a thermally driven resonant beam by using heavy doping. Fourth, using the SOI and anodic bonding processes limits the size of the film, making it difficult to make the pressure-sensitive film into a thin and small uniform film, which is not conducive to the miniaturization of the pressure sensor and the improvement of sensitivity.

[0004] In view of this, there is an urgent need for a preparation method of a resonant pressure sensor with low process cost, high sensitivity, and strong anti-interference ability of the resonant pressure sensor. Summary of the Invention

[0005] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a resonant pressure sensor and a preparation method thereof, which are used to solve the problems of high preparation process cost, low sensitivity, and weak anti-interference ability of the resonant pressure sensor in the prior art.

[0006] To achieve the above purpose and other related purposes, the present invention provides a preparation method of a resonant pressure sensor, including the following steps:

[0007] Provide a substrate, and form at least one pickup resistor and a drive resistor spaced apart from the pickup resistor on the upper surface layer of the substrate;

[0008] Form at least one resonant structure on the upper surface layer of the substrate. The resonant structure includes a resonant beam and a vibration gap. The resonant beam includes a first beam, a second beam spaced apart from each other, and an intermediate beam connecting the first beam and the second beam. The drive resistor is located on the upper surface layer of the first beam, the resonant resistor is located on the upper surface layer of the second beam, and the vibration gap includes an etching groove surrounding the resonant beam and a bottom cavity located below the resonant beam and communicating with the etching groove;

[0009] Form a sacrificial layer on the upper surface of the substrate to cover the opening of the vibration gap and the upper surface of the resonant beam, and the edge of the sacrificial layer is spaced apart from the opening of the vibration gap by a first preset distance, and form a sealing shell to cover the exposed surface of the sacrificial layer;

[0010] Form a groove opening from the bottom surface of the substrate directly below the resonant structure, and the bottom of the groove is spaced apart from the bottom of the vibration gap by a second preset distance;

[0011] Remove the sacrificial layer, and a sealed cavity is formed by enclosing the sealed housing and the vibration gap.

[0012] Optionally, the substrate includes a single crystal silicon substrate.

[0013] Optionally, before forming the resonant structure, it further includes the step of forming a plurality of lead regions respectively electrically connected to the drive resistor and the pickup resistor.

[0014] Optionally, after forming the sealed cavity, it further includes the step of forming a pad in ohmic contact with the lead region at one end of the lead region away from the drive resistor and the pickup resistor.

[0015] Optionally, before forming the pickup resistor, it further includes the step of forming a barrier layer in the substrate, the upper surface of the barrier layer coincides with the upper surface of the substrate and the bottom of the barrier layer is not higher than the bottom of the vibration gap.

[0016] Optionally, forming the resonant structure includes the following steps: forming a patterned mask layer on the upper surface of the substrate, forming the etching groove in the substrate based on the patterned mask layer, and at the same time the etching groove defines a resonant beam region, forming the bottom cavity penetrating the resonant beam region at the bottom of the etching groove, and the remaining part of the resonant beam region above the bottom cavity serves as the resonant beam.

[0017] Optionally, the size of the projection of the groove in the vertical direction is not less than the size of the projection of the region where the resonant structure is located in the vertical direction.

[0018] Optionally, after forming the sealed housing, before removing the sacrificial layer, it further includes the step of forming a release hole on the sealed housing.

[0019] Optionally, after removing the sacrificial layer, it further includes the step of forming a vacuum seal plug filling the release hole on the sealed housing.

[0020] The present invention also provides a resonant pressure sensor, and the resonant pressure sensor is prepared by using the preparation method of the resonant pressure sensor according to any one of the above, including:

[0021] A substrate;

[0022] A pickup resistor and a drive resistor, located on the upper surface layer of the substrate, and the pickup resistor and the drive resistor are arranged at intervals;

[0023] A resonant structure is located on the upper surface layer of the substrate. The resonant structure includes a resonant beam and a vibration gap. The resonant beam includes a first beam and a second beam arranged at intervals, and an intermediate beam connecting the first beam and the second beam. The drive resistor is located on the upper surface layer of the first beam, and the resonant resistor is located on the upper surface layer of the second beam. The vibration gap includes an etching groove surrounding the resonant beam and a bottom cavity at the bottom of the etching groove. The bottom cavity is communicated with the etching groove;

[0024] A sealing shell covers the opening of the vibration gap and the upper surface of the resonant beam, and the inner side wall of the sealing shell is spaced from the opening of the vibration gap by a first preset distance;

[0025] A groove is located directly below the resonant structure and opens from the bottom surface of the substrate. The bottom of the groove is spaced from the bottom of the vibration gap by a second preset distance;

[0026] A sealed cavity is formed by enclosing the sealing shell and the vibration gap.

[0027] As described above, the resonant pressure sensor and its manufacturing method of the present invention have the following beneficial effects: Based on the substrate made of single-crystalline silicon material, the problem of controllable processing of the structure size of the resonant beam structure on a non-SOI silicon wafer is solved by using the single-sided bulk micromachining technology of a single silicon wafer. On this basis, combined with the traditional double-sided bulk micromachining technology, the sensitive film is successfully prepared. The shape and size of the sensitive film are controllable. The sealed cavity surrounding the resonant structure is formed by using the surface process, realizing the integrated integration of multiple in-plane differential resonant structures and sealed cavities on a single chip. Compared with the process of the resonant pressure sensor structure prepared by using an expensive SOI silicon wafer combined with the bonding process in the past, the size of the sensor chip is effectively reduced, the process flow is simplified, the process cost is reduced, and the sensitivity and anti-interference ability of the resonant pressure sensor are improved. Description of the Drawings

[0028] Figure 1 It shows a schematic flow chart of the manufacturing method of the resonant pressure sensor of the present invention.

[0029] Figure 2 It shows a schematic structural diagram after forming a barrier layer in the manufacturing method of the resonant pressure sensor of the present invention.

[0030] Figure 3 It shows a schematic structural diagram after forming a lead resistor region in the manufacturing method of the resonant pressure sensor of the present invention.

[0031] Figure 4 It shows a schematic structural diagram after forming a mask layer and a first protective layer in the manufacturing method of the resonant pressure sensor of the present invention.

[0032] Figure 5 Schematic diagram of the structure after forming the etching groove in the preparation method of the resonant pressure sensor of the present invention.

[0033] Figure 6 Schematic diagram of the structure after forming the gap part in the preparation method of the resonant pressure sensor of the present invention.

[0034] Figure 7 Schematic diagram of the structure after forming the resonant beam in the preparation method of the resonant pressure sensor of the present invention.

[0035] Figure 8 Schematic diagram of the structure after forming the first sacrificial material layer in the preparation method of the resonant pressure sensor of the present invention.

[0036] Figure 9 Schematic diagram of the structure after forming the sacrificial layer in the preparation method of the resonant pressure sensor of the present invention.

[0037] Figure 10 Schematic diagram of the structure after forming the sealing shell in the preparation method of the resonant pressure sensor of the present invention.

[0038] Figure 11 Schematic diagram of the structure after forming the groove in the preparation method of the resonant pressure sensor of the present invention.

[0039] Figure 12 Schematic diagram of the structure after forming the vacuum sealing plug in the preparation method of the resonant pressure sensor of the present invention.

[0040] Figure 13 Schematic diagram of the structure after forming the pad in the preparation method of the resonant pressure sensor of the present invention.

[0041] Figure 14 Schematic diagram of the structure of the resonant pressure sensor of the present invention.

[0042] Figure 15 Schematic diagram of a partial structure of the resonant pressure sensor of the present invention.

[0043] Description of component labels

[0044] 1 Substrate

[0045] 11 Mask layer

[0046] 111 First passivation layer

[0047] 112 First low-stress layer

[0048] 113 Second passivation layer

[0049] 12 First protective layer

[0050] 121 Third passivation layer

[0051] 122 Second low-stress layer

[0052] 123 Fourth passivation layer

[0053] 13 First isolation layer

[0054] 14 Second isolation layer

[0055] 15 Sixth passivation layer

[0056] 2 Barrier layer

[0057] 21 Barrier groove

[0058] 22 Insulating layer

[0059] 23 Filling layer

[0060] 3 Lead resistance area

[0061] 4 Resonant structure

[0062] 41 Resonant beam

[0063] 411 First beam

[0064] 412 Second beam

[0065] 413 Intermediate beam

[0066] 42 Vibration gap

[0067] 421 Etching groove

[0068] 421a Second protective layer

[0069] 422 Bottom cavity

[0070] 423 Gap part

[0071] 43 Resonant beam area

[0072] 5 Sacrificial layer

[0073] 51 First sacrificial material layer

[0074] 52 Second sacrificial material layer

[0075] 6 Sealing shell

[0076] 61 Release hole

[0077] 62 Vacuum sealing plug

[0078] 7 Groove

[0079] 8 Sensitive film

[0080] 9 Sealing cavity

[0081] 10 Pad Specific implementation manners

[0082] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0083] Please refer to Figures 1 to 15 . It should be noted that the structures, ratios, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those skilled in the art to understand and read, and are not used to limit the implementation conditions of the present invention. Therefore, they do not have any technical essence. Any modification of the structure, change of the proportional relationship, or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope that can be covered by the technical content disclosed in the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle", and "one" cited in this specification are only for the convenience of clear description and are not used to limit the implementation scope of the present invention. Any change or adjustment of their relative relationships, without substantial change in the technical content, should also be regarded as the implementation scope of the present invention.

[0084] Embodiment 1

[0085] This embodiment provides a preparation method of a resonant pressure sensor. As Figure 1 shown, it is a schematic flow chart of the preparation method of the resonant pressure sensor, including the following steps:

[0086] S1: Provide a substrate, and form at least one pickup resistor and a drive resistor spaced from the pickup resistor on the upper surface layer of the substrate;

[0087] S2: Form at least one resonant structure on the upper surface layer of the substrate. The resonant structure includes a resonant beam and a vibration gap. The resonant beam includes a first beam and a second beam spaced apart and an intermediate beam connecting the first beam and the second beam. The drive resistor is located on the upper surface layer of the first beam, the resonant resistor is located on the upper surface layer of the second beam, and the vibration gap includes an etching groove surrounding the resonant beam and a bottom cavity located below the resonant beam and communicating with the etching groove;

[0088] S3: Form a sacrificial layer covering the opening of the vibration gap and the upper surface of the resonant beam and having an edge spaced from the opening of the vibration gap by a first preset distance on the upper surface of the substrate, and form a sealing shell covering the exposed surface of the sacrificial layer;

[0089] S4: Remove the sacrificial layer, and a sealed cavity is formed by enclosing the sealed shell and the vibration gap;

[0090] S5: A groove opening from the bottom surface of the substrate is formed directly below the resonant structure, and the bottom of the groove is spaced from the bottom of the vibration gap by a second preset distance.

[0091] Specifically, please refer to Figures 2 - 3 , perform step S1 to provide a substrate 1, and form at least one pick-up resistor (not shown) and a driving resistor (not shown) spaced from the pick-up resistor on the upper surface of the substrate 1.

[0092] As an example, the substrate 1 includes a single-crystal silicon substrate or other suitable substrates.

[0093] Specifically, the crystal plane orientation of the substrate 1 is (111).

[0094] Specifically, the thickness range of the substrate 1 is 400 μm to 500 μm. In this embodiment, the thickness of the substrate 1 is 450 μm.

[0095] As an example, as Figure 2 shown, it is a schematic structural diagram after forming the barrier layer 2. Before forming the pick-up resistor and the driving resistor, it further includes the step of forming a barrier layer 2 in the substrate 1, the upper surface of the barrier layer 2 coincides with the upper surface of the substrate 1 and the bottom of the barrier layer 2 is not higher than the bottom of the vibration gap 42.

[0096] As an example, forming the barrier layer 2 includes the following steps: forming a patterned oxide layer (not shown) on the upper surface of the substrate 1, forming a barrier groove 21 in the substrate 1 based on the patterned oxide layer, and sequentially forming an insulating layer 22 and a filling layer 23 filling the barrier groove 21 in the barrier groove 21 to obtain the barrier layer 2.

[0097] Specifically, the material of the oxide layer includes silicon dioxide or other suitable materials.

[0098] Specifically, the method of forming the oxide layer includes thermal oxidation or other suitable methods.

[0099] Specifically, the thickness range of the oxide layer is In this embodiment, the thickness of the oxide layer is

[0100] Specifically, patterning the oxide layer is a conventional technical means and will not be elaborated here.

[0101] Specifically, the method of forming the barrier groove 21 includes deep reactive ion etching or other suitable methods.

[0102] Specifically, the method for forming the insulating layer 22 includes low-pressure chemical vapor deposition or other suitable methods.

[0103] Specifically, the material of the insulating layer 22 includes silicon nitride or other suitable materials.

[0104] Specifically, the formed insulating layer 22 covers the inner wall of the barrier groove 21.

[0105] Specifically, the method for forming the filling layer 23 includes low-pressure chemical vapor deposition or other suitable methods.

[0106] Specifically, the material of the filling layer 23 includes polysilicon or other suitable materials.

[0107] Specifically, the thickness of the formed barrier layer 2 is not less than 20 μm. In this embodiment, the thickness of the barrier layer 2 is 25 μm.

[0108] Specifically, when the performance of the resonant pressure sensor is satisfied, the number of the barrier layers 2 can be selected according to the actual situation and is not limited herein. In this embodiment, the number of the barrier layers 2 is two.

[0109] As an example, before forming the resonant structure 4, it further includes the step of forming a plurality of lead regions respectively electrically connected to the drive resistor and the pick-up resistor.

[0110] Specifically, as Figure 3 shown, it is a schematic structural diagram after forming the lead resistor region 3. Forming the pick-up resistor, the drive resistor and the lead region includes the following steps: forming a patterned hard film layer (not shown) on the upper surface of the substrate 1 to define the lead resistor region 3 where the pick-up resistor, the drive resistor and the lead 21 are located, and forming the pick-up resistor, the drive resistor and the lead region in the lead resistor region 3.

[0111] Specifically, the method for forming the pick-up resistor includes ion implantation or other suitable methods; the method for forming the drive resistor includes ion implantation or other suitable methods; the method for forming the lead region includes ion implantation or other suitable methods.

[0112] Specifically, the implanted ions used in the ion implantation method for forming the pick-up resistor, the drive resistor and the lead region include boron ions or other suitable ions.

[0113] Specifically, after forming the pickup resistor, the drive resistor, and the lead region by boron ion implantation, it further includes the steps of performing boron main diffusion in an oxygen environment to repair the damage to the crystal lattice caused by ion implantation and activate the boron ions.

[0114] Specifically, when the performance of the resonant pressure sensor is satisfied, the energy and concentration of ion implantation can be selected according to actual situations and are not limited herein.

[0115] Specifically, please refer to Figures 4 - 7 , perform step S2, and form at least one resonant structure 4 on the upper surface layer of the substrate 1. The resonant structure 4 includes a resonant beam 41 and a vibration gap 42. The resonant beam 41 includes a first beam 411 and a second beam 412 arranged at intervals and an intermediate beam 413 connecting the first beam 411 and the second beam 412. The drive resistor is located on the upper surface layer of the first beam 411, the resonant resistor is located on the upper surface layer of the second beam 412, and the vibration gap 42 includes an etching groove 421 surrounding the resonant beam 41 and a bottom cavity 422 located below the resonant beam 41 and communicating with the etching groove 421.

[0116] As an example, as Figures 4 - 7 shown, they are respectively a schematic structural diagram after forming the mask layer 11, a schematic structural diagram after forming the etching groove 421, a schematic structural diagram after forming the gap portion 423, and a schematic structural diagram after forming the resonant beam 41. Forming the resonant structure 4 includes the following steps: forming a patterned mask layer 11 on the upper surface of the substrate 1, forming the etching groove 421 in the substrate 1 based on the patterned mask layer 11, and at the same time, the etching groove 421 defines a resonant beam region 43. Form the bottom cavity 422 penetrating the resonant beam region 43 at the bottom of the etching groove 421, and the remaining part in the resonant beam region 43 above the bottom cavity 422 serves as the resonant beam 41.

[0117] Specifically, before forming the bottom cavity 422, it further includes the step of forming a gap portion 423 with an opening size smaller than that of the etching groove 421 from the bottom opening of the etching groove 421.

[0118] Specifically, the bottom cavity 422 is obtained by further etching the substrate 1 below the resonant beam region 43 based on the gap portion 423.

[0119] Specifically, a first protective layer 12 covering the lower surface of the substrate 1 is also formed while forming the mask layer 11.

[0120] Specifically, the mask layer 11 includes a first passivation layer 111, a first low-stress layer 112, and a second passivation layer 113 that are stacked in sequence; the first protection layer 12 includes a third passivation layer 121, a second low-stress layer 122, and a fourth passivation layer 123 that are stacked in sequence.

[0121] Specifically, the method for forming the mask layer 11 includes chemical vapor deposition, physical vapor deposition, or other suitable methods; the method for forming the first protection layer 12 includes chemical vapor deposition, physical vapor deposition, or other suitable methods.

[0122] Specifically, the material of the first passivation layer 111 includes tetraethoxysilane or other suitable materials; the material of the first low-stress layer 112 includes silicon nitride or other suitable materials; the material of the second passivation layer 113 includes tetraethoxysilane or other suitable materials; the material of the third passivation layer 121 includes tetraethoxysilane or other suitable materials; the material of the second low-stress layer 122 includes silicon nitride or other suitable materials; the material of the fourth passivation layer 123 includes tetraethoxysilane or other suitable materials.

[0123] Specifically, the thickness range of the first passivation layer 111 is The thickness range of the first low-stress layer 112 is The thickness range of the second passivation layer 113 is The thickness range of the third passivation layer 121 is The thickness range of the second low-stress layer 122 is The thickness range of the fourth passivation layer 123 is In this embodiment, the thickness of the first passivation layer 111 is The thickness of the first low-stress layer 112 is The thickness of the second passivation layer 113 is The thickness of the third passivation layer 121 is The thickness of the second low-stress layer 122 is The thickness range of the fourth passivation layer 123 is

[0124] Specifically, the method for forming the etching groove 421 includes reactive ion etching, deep reactive ion etching, or other suitable methods.

[0125] Specifically, the depth range of the formed etching groove 421 is 4 μm to 8 μm. In this embodiment, the depth of the etching groove 421 is 6 μm, and the depth here refers to the vertical distance between the opening and the bottom of the etching groove 421.

[0126] Specifically, forming the gap portion 423 includes the following steps: forming a second protective layer 421a covering the inner wall of the etching groove 421, removing the second protective layer 421a located at the bottom of the etching groove 421, and forming the gap portion 423 communicating with the etching groove 421 from the bottom opening of the etching groove 421.

[0127] Specifically, the second protective layer 421a includes a third low-stress layer and a fifth passivation layer that sequentially cover the inner wall of the etching groove 421.

[0128] Specifically, the material of the third low-stress layer includes silicon nitride or other suitable materials; the material of the fifth passivation layer includes tetraethoxysilane or other suitable materials.

[0129] Specifically, the thickness range of the third low-stress layer is The thickness range of the fifth passivation layer is In this embodiment, the thickness of the third low-stress layer is The thickness of the fifth passivation layer 411b is

[0130] Specifically, the method for removing the second protective layer 421a includes reactive ion etching or other suitable methods.

[0131] Specifically, the method for forming the gap portion 423 includes deep reactive ion etching or other suitable methods.

[0132] Specifically, the depth range of the gap portion 423 is 2 μm to 4 μm. In this embodiment, the depth of the gap portion 423 is 3 μm, and the depth here refers to the vertical distance between the opening and the bottom of the gap portion 423.

[0133] Specifically, the method for forming the bottom cavity 422 based on the gap portion 423 includes anisotropic wet etching or other suitable methods.

[0134] Specifically, the etching solution used for forming the bottom cavity 422 by anisotropic wet etching includes tetramethylammonium hydroxide, potassium hydroxide, or other suitable etching solutions.

[0135] Specifically, the temperature range for forming the bottom cavity 422 by anisotropic wet etching is 70°C to 90°C. In this embodiment, the temperature used is 80°C.

[0136] Specifically, when removing the mask layer 11, it also includes removing the first protective layer 12.

[0137] Specifically, the method for removing the mask layer 11 includes dry etching, wet etching, chemical mechanical polishing or other suitable methods; the method for removing the first protective layer 12 includes dry etching, wet etching, chemical mechanical polishing or other suitable methods.

[0138] Specifically, the etching grooves 421 are arranged along the <211> crystal orientation.

[0139] Specifically, when the performance of the resonant pressure sensor is satisfied, the dimensions of the first beam 411 can be selected according to actual conditions and are not limited herein; the dimensions of the second beam 412 can be selected according to actual conditions and are not limited herein; the dimensions of the intermediate beam 413 can be selected according to actual conditions and are not limited herein.

[0140] Specifically, the drive resistor and the pick-up resistor are respectively located on the upper surfaces of the first beam 411 and the second beam 412, and both ends of the drive resistor and the pick-up resistor are electrically connected to the pads through the lead regions doped with high-concentration boron ions.

[0141] Specifically, when the performance of the resonant pressure sensor is satisfied, the number of the resonant structures 3 can be selected according to actual conditions and is not limited herein. In this embodiment, the number of the resonant structures 4 is two, and the two resonant structures 4 are arranged in parallel on the upper surface of the substrate 1. The two resonant structures 4 are respectively located on both sides of the center point of the substrate 1, and the two resonant structures 4 respectively detect the tensile stress and the corresponding compressive stress in specific regions on the substrate 1, so as to realize differential pressure detection output.

[0142] Specifically, in the resonant structure 4, there is also a step of forming a fixing beam (not shown) for fixing the resonant beam 41.

[0143] Specifically, please refer to Figures 8 - 10 , perform the step S3, form a sacrificial layer 5 on the upper surface of the substrate 1 to cover the opening of the vibration gap 42 and the upper surface of the resonant beam 41, and the edge of the sacrificial layer 5 is spaced from the opening of the vibration gap 42 by a first preset distance, and form a sealing shell 6 to cover the exposed surface of the sacrificial layer 5.

[0144] Specifically, as Figures 8 - 9As shown, they are respectively the structural schematic diagrams after forming the first sacrificial material layer 51 and after forming the sacrificial layer 5. The steps of forming the sacrificial layer 5 include: sequentially forming on the upper surface of the substrate 1 a first sacrificial material layer 51 covering the opening of the vibration gap 42 and the upper surface of the resonant beam 41, and a second sacrificial material layer 52 covering the exposed surface of the first sacrificial material layer 51 and having an edge spaced from the sidewall of the first sacrificial material layer 51 by a third preset distance, so as to obtain the sacrificial layer 5, wherein the edge of the second sacrificial material layer 52 is spaced from the opening of the vibration gap 42 by a first preset distance.

[0145] Specifically, before forming the sacrificial layer 5, steps of forming the first isolation layer 13 on the upper surface of the substrate 1 and forming the second isolation layer 14 on the lower surface of the substrate 1 are further included.

[0146] Specifically, the first isolation layer 13 and the first sacrificial layer 61 also fill the vibration gap 42.

[0147] Specifically, the material of the first isolation layer 13 includes silicon nitride or other suitable materials; the material of the second isolation layer 14 includes silicon nitride or other suitable materials.

[0148] Specifically, when forming the second sacrificial material layer 52, a step of forming a sixth passivation layer 15 covering the surface of the second isolation layer 14 is further included.

[0149] Specifically, the thickness range of the first isolation layer 13 is The thickness range of the first sacrificial material layer 51 is The thickness range of the second isolation layer 13 is The thickness range of the second sacrificial material layer 52 is In this embodiment, the thickness of the first isolation layer 13 is The thickness of the first sacrificial material layer 51 is The thickness of the second isolation layer 14 is The thickness range of the second sacrificial material layer 52 is

[0150] Specifically, as Figure 10 shown, it is the structural schematic diagram after forming the sealing shell 6. The method of forming the sealing shell 6 includes chemical vapor deposition, physical vapor deposition or other suitable methods.

[0151] Specifically, the material of the sealing shell 6 includes polysilicon or other suitable materials.

[0152] Specifically, the thickness range of the sealing shell 6 is In this embodiment, the thickness of the sealing shell 6 is

[0153] Specifically, please refer to Figure 11 , perform step S5, and form a groove 7 opening from the bottom surface of the substrate 1 directly below the resonant structure 4. The bottom of the groove 7 is spaced from the bottom of the vibration gap 32 by a second preset distance.

[0154] As an example, the size of the projection of the groove 7 in the vertical direction is not less than the size of the projection of the area where the resonant structure 4 is located in the vertical direction. The area where the resonant structure 4 is located here refers to the area where all the resonant structures 4 formed in the resonant pressure sensor are located.

[0155] Specifically, before forming the groove 7, there is also a step of etching the second isolation layer 14 and the sixth passivation layer 15 to define the area where the groove 7 is located.

[0156] Specifically, the method for removing the second isolation layer 14 includes reactive ion etching or other suitable methods; the method for removing the sixth passivation layer 15 includes reactive ion etching or other suitable methods.

[0157] Specifically, the remaining part of the substrate 1 (as shown by the dotted line in Figure 11 ) surrounding the resonant structure 4 after forming the groove 7 serves as the sensitive film 8 of the resonant pressure sensor.

[0158] Specifically, by forming the groove 7 in the substrate 1 to obtain the sensitive film 8, the thickness and shape of the formed sensitive film 8 are controllable, simplifying the formation process of the resonant pressure sensor and improving the sensitivity and anti-interference ability of the device.

[0159] Specifically, as shown in Figure 11 , which is a schematic structural diagram after forming the groove 7, the method for forming the groove 7 includes deep reactive ion etching or other suitable methods.

[0160] Specifically, please refer to Figures 12 - 13 , perform step S5, remove the sacrificial layer 5, and the sealing shell 6 and the vibration gap 32 enclose to form a sealed cavity 9.

[0161] As an example, after forming the sealing shell 6 and before removing the sacrificial layer 5, there is also a step of forming a release hole 61 on the sealing shell 6.

[0162] Specifically, the release hole 61 is used to remove the sacrificial layer 5.

[0163] Specifically, the method for removing the sacrificial layer 5 includes dry etching or other suitable methods.

[0164] Specifically, the method for forming the release hole 61 includes dry etching or other suitable methods.

[0165] As an example, after removing the sacrificial layer 5, it further includes the step of forming a vacuum sealing plug 62 on the sealing shell 6 to fill the release hole 61.

[0166] Specifically, as Figure 12 shown, it is a schematic structural diagram after forming the vacuum sealing plug 62. The method for forming the vacuum sealing plug 62 includes chemical vapor deposition, physical vapor deposition, or other suitable methods.

[0167] Specifically, the material of the vacuum sealing plug 62 includes tetraethoxysilane or other suitable materials.

[0168] Specifically, the thickness range of the vacuum sealing plug 62 is In this embodiment, the thickness of the vacuum sealing plug 62 is

[0169] Specifically, the vacuum sealing plug 62 is used to seal the sealing cavity 9.

[0170] As an example, after forming the sealing cavity 9, it further includes the step of forming a pad 10 in ohmic contact with the lead region at one end of the lead region away from the drive resistor and the pick-up resistor.

[0171] Specifically, as Figure 13 shown, it is a schematic structural diagram after forming the pad 10. The method for forming the pad 10 includes magnetron sputtering or other suitable methods.

[0172] Specifically, before forming the pad 10, it further includes the step of etching the first isolation layer 13 on the upper surface of the substrate 1 to expose the external connection window of the pad 10.

[0173] Specifically, the material of the pad 10 includes aluminum or other suitable materials.

[0174] Specifically, when the performance of the resonant pressure sensor is satisfied, the number of the pads 10 can be selected according to the actual situation and is not limited here.

[0175] Specifically, the preparation method of the resonant pressure sensor in this embodiment is applicable to the processing of the pressure sensor based on the in-plane differential type of the resonant structure 4, and is also applicable to the processing of the pressure sensor based on the out-of-plane differential type of the resonant structure 4, and can be selected according to the actual process requirements.

[0176] The preparation method of the resonant pressure sensor of this embodiment is based on the substrate 1 made of single-crystalline silicon. By using the single-wafer single-sided bulk micromachining technology, the processing problem of controllable structural dimensions of the resonant structure 4 on a non-SOI silicon wafer is solved. On this basis, combined with the traditional double-sided bulk micromachining technology, the sensitive diaphragm 8 with controllable shape and thickness is successfully prepared. By using the surface process, the sealing cavity 9 that seals the resonant structure 4 is formed. Compared with the process of the resonant pressure sensor structure prepared by combining the expensive SOI silicon wafer and the bonding process, the integrated integration of multiple in-plane differential resonant structures and the sealing cavity 9 on the substrate is realized, effectively reducing the size of the sensor chip, simplifying the process flow, reducing the process cost, and improving the device performance.

[0177] Embodiment 2

[0178] This embodiment provides a resonant pressure sensor, as Figures 14 - 15 shown, which are respectively the structural schematic diagram of the resonant pressure sensor and the partial structural schematic diagram of the resonant pressure sensor. The resonant pressure sensor is prepared by using the preparation method of the resonant pressure sensor described in Embodiment 1. The resonant pressure sensor includes: a substrate 1, a pick-up resistor, a drive resistor, a resonant structure 4, a sealing shell 6, a sealing cavity 9, and a groove 7. Among them,

[0179] The pick-up resistor and the drive resistor are located on the upper surface layer of the substrate 1 and the pick-up resistor and the drive resistor are arranged at intervals; the resonant structure 3 is located on the upper surface layer of the substrate 1. The resonant structure 4 includes a resonant beam 41 and a vibration gap 42. The resonant beam 41 includes a first beam 411, a second beam 412 arranged at intervals, and an intermediate beam 413 connecting the first beam 411 and the second beam 412. The drive resistor is located on the upper surface layer of the first beam 411, the resonant resistor is located on the upper surface layer of the second beam 412. The vibration gap 42 includes an etching groove 421 surrounding the resonant beam 41 and a bottom cavity 422 located at the bottom of the etching groove 421. The bottom cavity 422 is communicated with the etching groove 421;

[0180] The sealing shell 6 covers the opening of the vibration gap 42 and the upper surface of the resonant beam 41, and the inner side wall of the sealing shell 6 is spaced from the opening of the vibration gap 321 by a first preset distance; the sealing shell 6 and the vibration gap 42 enclose to form a sealing cavity 9; the groove 7 is located directly below the resonant structure 4 and opens from the bottom surface of the substrate 1, and the bottom of the groove 7 is spaced from the bottom of the vibration gap by a second preset distance.

[0181] Specifically, a barrier layer 2 is further included in the resonant pressure sensor.

[0182] Specifically, the blocking layer 2 is used to block excessive vibration deformation of the resonant beam 41 in the vibration gap 42.

[0183] Specifically, the resonant pressure sensor further includes a plurality of lead regions respectively electrically connected to the drive resistor and the pick-up resistor.

[0184] Specifically, the pad 10 is electrically connected to the resonant beam 41 through the lead region, the pick-up resistor, and the drive resistor, and is used for exciting the resonant beam 41 and transmitting and detecting pick-up signals.

[0185] Specifically, the substrate 1 of the part surrounding the resonant structure 4 remaining after forming the groove 7 serves as the sensitive film 8 of the resonant pressure sensor.

[0186] Specifically, the sealing shell 6 is further provided with a release hole 61 and a vacuum sealing plug 62 filling the release hole 61.

[0187] Specifically, a fixed beam (not shown) for fixing the resonant beam 41 is further formed in the resonant structure 4.

[0188] The resonant pressure sensor of this embodiment is prepared by using the preparation method of the resonant pressure sensor described in Embodiment 1. By integrally forming the in-plane differential resonant structure 4, the sealing cavity 9, and the sensitive film 8 on the substrate 1 made of single-crystalline silicon material, compared with the process of the resonant pressure sensor structure prepared by the traditional expensive SOI silicon wafer bonding process, the size of the sensor chip is effectively reduced, and the device performance is improved.

[0189] In summary, for the resonant pressure sensor and its preparation method of the present invention, based on a substrate made of single-crystalline silicon material, the single-side bulk micromachining technology of single silicon wafer is used to solve the processing problem of controllable structural dimensions of the resonant beam structure on non-SOI silicon wafers. On this basis, combined with the traditional double-side bulk micromachining technology, a sensitive film is successfully prepared, and the shape and size of the sensitive film are controllable. The sealing cavity surrounding the resonant structure is formed by surface technology, realizing the in-plane differential resonant structure and the integration of the sealing cavity on a single chip. Compared with the process of the resonant pressure sensor structure prepared by the traditional expensive SOI silicon wafer bonding process, the size of the sensor chip is effectively reduced, the process flow is simplified, the process cost is reduced, and the sensitivity and anti-interference ability of the resonant pressure sensor are improved. Therefore, the present invention effectively overcomes various disadvantages in the prior art and has high industrial utilization value.

[0190] The above embodiments are only illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A preparation method of a resonant pressure sensor, characterized in that, It includes the following steps: Provide a substrate, and form at least one pickup resistor and a drive resistor spaced from the pickup resistor on the upper surface of the substrate; Form at least one resonant structure on the upper surface of the substrate. The resonant structure includes a resonant beam and a vibration gap. The resonant beam includes a first beam and a second beam spaced apart, and an intermediate beam connecting the first beam and the second beam. The drive resistor is located on the upper surface of the first beam, the pickup resistor is located on the upper surface of the second beam, and the vibration gap includes an etching groove surrounding the resonant beam and a bottom cavity located below the resonant beam and communicating with the etching groove; Form a sacrificial layer on the upper surface of the substrate to cover the opening of the vibration gap and the upper surface of the resonant beam, and the edge of the sacrificial layer is spaced from the opening of the vibration gap by a first preset distance, and form a sealing shell to cover the exposed surface of the sacrificial layer; Form a groove opening from the bottom surface of the substrate directly below the resonant structure, and the bottom of the groove is spaced from the bottom of the vibration gap by a second preset distance; Remove the sacrificial layer, and the sealing shell and the vibration gap enclose to form a sealed cavity.

2. The manufacturing method of the resonant pressure sensor according to claim 1, characterized in that: The substrate includes a single-crystalline silicon substrate.

3. The manufacturing method of the resonant pressure sensor according to claim 1, characterized in that: Before forming the resonant structure, it further includes the step of forming a plurality of lead regions respectively electrically connected to the drive resistor and the pickup resistor.

4. The manufacturing method of the resonant pressure sensor according to claim 3, characterized in that: After forming the sealed cavity, it further includes the step of forming pads in ohmic contact with the lead regions at one end of the lead regions away from the drive resistor and the pickup resistor.

5. The manufacturing method of the resonant pressure sensor according to claim 1, characterized in that: Before forming the pickup resistor and the drive resistor, it further includes the step of forming a barrier layer in the substrate. The upper surface of the barrier layer coincides with the upper surface of the substrate, and the bottom of the barrier layer is not higher than the bottom of the vibration gap.

6. The manufacturing method of the resonant pressure sensor according to claim 1, characterized in that: Forming the resonant structure includes the following steps: form a patterned mask layer on the upper surface of the substrate, form the etching groove in the substrate based on the patterned mask layer, and at the same time the etching groove defines a resonant beam region, form the bottom cavity penetrating the resonant beam region at the bottom of the etching groove, and the remaining part of the resonant beam region above the bottom cavity serves as the resonant beam.

7. The manufacturing method of the resonant pressure sensor according to claim 1, characterized in that: The size of the projection of the groove in the vertical direction is not less than the size of the projection of the region where the resonant structure is located in the vertical direction.

8. The manufacturing method of the resonant pressure sensor according to claim 1, characterized in that: After forming the sealing shell and before removing the sacrificial layer, it further includes the step of forming a release hole on the sealing shell.

9. The preparation method of the resonant pressure sensor according to claim 8, wherein: After removing the sacrificial layer, it further includes the step of forming a vacuum sealing plug filling the release hole on the sealing shell.

10. A resonant pressure sensor, characterized in that, The resonant pressure sensor is prepared by using the preparation method of the resonant pressure sensor according to any one of claims 1 to 9, and includes: A substrate; A pickup resistor and a drive resistor, located on the upper surface of the substrate, and the pickup resistor and the drive resistor are spaced apart; A resonant structure, located on the upper surface layer of the substrate, the resonant structure includes a resonant beam and a vibration gap, the resonant beam includes a first beam and a second beam arranged at intervals and an intermediate beam connecting the first beam and the second beam, the drive resistor is located on the upper surface layer of the first beam, the resonant resistor is located on the upper surface layer of the second beam, the vibration gap includes an etching groove surrounding the resonant beam and a bottom cavity located at the bottom of the etching groove, and the bottom cavity is communicated with the etching groove; A sealing shell, covering the opening of the vibration gap and the upper surface of the resonant beam, and the inner side wall of the sealing shell is spaced from the opening of the vibration gap by a first preset distance; A groove, located directly below the resonant structure and opening from the bottom surface of the substrate, and the bottom of the groove is spaced from the bottom of the vibration gap by a second preset distance; A sealed cavity, the sealed cavity is formed by enclosing the sealing shell and the vibration gap.

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